Electric initiator and method of making same



Oct. 3, 1961 J. A. DOUGHTY ELECTRIC INITIATOR AND METHOD OF MAKING SAME Filed Oct. 22, 1953 FIG.1.

ATTORNEYS fm .4 m

3,002,457 ELECTRIC INITIATOR AND METHOD OF MAKING SAME "John A. Doughty, Fayetteville, Ark., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Oct. 22, 1953, Ser. No. 387,820 7 Claims. (Cl. 102-70.2)

' The present invention relates to electric initiators for use in the firing circuits of fuzes or the like and more particularly, the invention relates to electric initiators in which soft crystalline graphite having an oriented crystalline structure is employed as the conductive bridge across a pair of spaced lead wires set in a plug of insulating material. In .prior art initiators wherein colloidal graphite and water or oil is applied to the plug face in the usual manner, the graphite has random crystalline structure which results in marked thermal, electrical and magnetic anisotropies, thus the resistance value of the conductive bridge may vary considerably from plug to plug and cause erratic performance characteristics.

In the present invention soft crystalline graphite of high purity is applied to the plug face under shearing or frictional pressure which results in the graphite crystals assuming a (100) plane orientation parallel to the substrate or plug face. In such orientation the graphite crystals provide a conductive element or bridge which has maximum mechanical strength and which by bufiing or polishing may be caused to provide a desired resistance to the passage of current therethrough.

It is, thus, possible to provide a plurality of plugs having identical resistances where tests are made to ascertain the igniting qualities of a variety of ignition mixtures for Mes.

It is also possible to provide a conductive bridge for an electric initiator in which the resistance is brought to exactly the value desired for producing optimum results when employed with a given firing circuit, it being understood that the various types of firing circuits produce optimum results only when a resistance favorable to the particular circuit is employed.

An object of the present invention is to provide a new and improved conductive bridge for an electric initiator in which the resistance thereof is held within close limits for use with a given firing circuit.

Another object is to provide a new and improved conductive bridge for an electric initiator having a pair of spaced electrodes and in which the bridge is formed of crystalline graphite wherein the crystals are oriented with the (100) plane thereof parallel to a substrate, the current passing through the graphite to ignite an initiator charge.

Still another object is to provide a new and improved conductive bridge for an electric initiator formed of crystalline graphite and wherein uniformity of resistance is attainable in each bridge of a plurality thereof.

Gther objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing wherein:

FIG. 1 is a vertical sectional view through an electric initiator showing the manner of causing (100) plane orientation of the graphite crystals applied thereto;

FIG. 2 is a schematic plan view of the device of FIG. 1, and

FIG. 3 is a view similar to FIG. 1 and showing the bufi'ing operation.

Referring more particularly to the drawings wherein like numerals indicate like parts throughout the several r 3,062,457. Patented Oct. 3, 1961 views, 10 indicates an initiator plug formed of insulating material and having flat face or substrate 11. A pair of electrodes 12 and 13v pass through the plug 10, one'end of each electrode being flush with face 11. A quantity of pure crystalline graphite 14 is applied to face 11 and bridging the electrodes 12 and 13. Frictional or shearing pressure is applied to graphite 14, pressure being applied by a device 15 in direction of arrow A while moving across the graphite 14 in the direction B.

It is, of course, understood that the graphite crystals, when applied to face 11 are oriented in random. directions. Such random orientation indicated at R has the efiect of causing erratic performance of the graphite bridge, the resistance of the bridge varying in accordance with the random orientation of the graphite crystals.

In order to prevent such random orientation of the graphite crystals, the device 15, as aforesaid, is employed to provide frictional pressure thereto thus to cause each of the graphite crystals to assume an orientation indicated at P whereby the plane of each crystal is parallel to face 11. In this orientation the graphite crystals provide maximum mechanical strength, and all the effects brought about by the electrical, thermal, and magnetic anisotropies of the graphite serve to strengthen the (100) plane orientation.

In order to provide the graphite bridge 14 with a desired resistance value, an ammeter AM and a source of low constant potential such as battery BA, as shown in FIG. 3, are connected across electrodes 12 and 13 whereupon a buffing wheel or other such device W is applied to the graphite 14, the graphite being polished or Worn away until the resistance of the graphite has reached a desired value, as indicated on ammeter AM.

It is important, when testing the ignition characteristics of different igniting compounds, to provide a conductive bridge of uniform resistance for each of the compounds, thus the foregoing buffing or polishing operation is of particular benefit in assuring the uniformity of resistance in the plurality of conductive bridges employed in such tests.

It has, also, been demonstrated in tests that specific firing circuits for the conductive bridges of fuzes require for optimum results a conductive bridge of specific resistance. In employing the oriented crystalline graphite bridge of the present invention, the resistance thereof may be readily brought to a desired value as has been heretofore set forth.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

l. The method of preparing a conductive bridge on the substrate of an electric initiator comprising the steps of applying a quantity of crystalline graphite to the substrate, the graphite having normally a random orientation of the crystals, and applying to said graphite after application thereof a pressure against and across the substrate whereby the crystals are oriented in a preferred direction.

2. The method of preparing a conductive bridge on the substrate of an electric initiator comprising, the steps of applying a quantity of soft crystalline graphite to the substrate, said graphite having random crystal orientation, and applying to said graphite after application thereof a shearing pressure across said substrate thereby to orient the graphite crystals with the (100) plane thereof parallel to the substrate.

3. The method of providing a conductive bridge having a desired resistance on the substrate of an electric initi- 3 ator' comprising the steps of applying a quantity of soft crystalline graphite to the substrate, said graphite having random crystal orientation, applying to said graphite a shearing pressure against and across said substrate whereby the graphite crystals are oriented with the (109) plane substantially parallel to the substrate, measuring the elec-' trical resistance across said graphite, and cutting said graphite during said measuring until the resistance there of reaches a desired value.

4. An electric initiator for a fuze comprising, in combination, a plug having a flat face thereon, a quantity of pure crystalline graphite on said face, said graphite having the crystals oriented with the (100) plane thereof parallel to said face, and means for passing an electrical current through said graphite.

5. An electric initiator comprising, in combination, a plug having a face thereon, a pair of spaced parallel electrodes passing through said plug and having one end of each electrode flush with said face, and a quantity of crystalline graphite applied to said face and bridging said 20 electrodes, the crystals of said graphite being oriented with the (100) plane thereof substantially parallel to the face.

8,002,415 /a u a a 6. The method of providing a conductive bridge having a desired resistance on the substrate of an electrical initiator comprising the steps of applying a quantity of graphite to the substrate, said graphite having normally a random crystal orientation, orienting the crystals in said graphite in a preferred direction, and buffing said graphite until the resistance. thereof reaches a desired value.

7. The method of preparing a conductive bridge having a desired resistance on the substrate of an electric initiator comprising the steps of applying a quantity of graphite to the substrate, said graphite having'normally a random crystal orientation, applying to said graphite after application thereof a shearing pressure against and across said substrate thereby orienting the crystals in-said gra'plb ite in a preferred direction, and boiling said graphite until the resistance thereof reaches a desired value.

References Cited in the file of this patent UNITED STATES PATENTS 39,542 Beardslee' Aug. 18, 1863 

